A binocular telescope usually is a long-range optical device which is used to observe objects with a certain magnification. With binocular telescopes, the observed objects can be seen with both eyes through separate optical paths that are provided in respective separate housing parts, the tubes. For this purpose, the two optical paths shall be aligned exactly in parallel to each other, preferably with an angular deviation of not more than 10′ for any eye spacing.
For adjusting a binocular to the eye spacing of a respective individual user, generally the two tubes which are connected to one another via folding bridges are folded through a common mechanical axis that forms a hinge axis. This allows a user to individually adapt the binocular telescope to his eye spacing which is also known as interpupillary distance IPD, for this see, for example, FIG. 2 of the accompanying drawings.
The folding bridges of a binocular generally function like a hinge. In case of a single folding bridge, the hinge or pivoting axis of the binoculars (folding axis) is already unambiguously defined by the hinge axis of the single folding bridge. In case of two folding bridges, the folding axis results from the common averaged axis of the two hinge axes of the two folding bridges. This means that the hinge axes of the two folding bridges have to be aligned very precisely to ensure a proper folding movement without unwanted friction or deformation forces. Otherwise, jamming may occur upon folding. In case of more than two folding bridges, this problem is still aggravated considerably.
In order to have the three hinge axes aligned, in case of three bridge elements, to form a common folding axis which ensures that the binocular alignment of the two optical paths as set is maintained upon folding, very high accuracy requirements are imposed on the manufacturing of the bridge elements. This results in high costs in the manufacturing of such binoculars having more than two folding bridges. The required eye-side 10′ of axial binocular alignment must be implemented on all mechanical interfaces of the individual bridge elements. If the alignment is not within the required eye-side 10′ parallelism, the binoculars will not be usable, or usability thereof may at least be strongly impaired.
This particularly applies when the binocular is exposed to mechanical and climatic stress which is typical for an outdoor device such as in the hunting sector. This means that the bridge elements must have a robust design so that the factory-set binocular alignment will not be impaired over the lifetime of the product, which requires high mechanical strengths in the configuration of the binocular telescope.
A single folding bridge might be unsuited for this purpose due to insufficient stability, and consequently generally at least two folding bridges are implemented in practice.
The further the two folding bridges are spaced axially from each other, the more stable the folding axis of the binoculars will be, and the more robust the product will be in terms of meeting the required binocular alignment.
In case of a third folding bridge in the middle, the additional hinge axis thereof at the folding axis will also have an impact on stability. The folding axis of the binoculars will therefore be overdetermined (three hinge axes), which imposes even significantly higher accuracy requirements on manufacturing than with only two hinge axes.
DE 2 316 955 describes a binocular telescope with adjustable use condition and packed condition and with common focusing of the two individual telescopes, in which two articulated bridges are arranged between the individual telescopes. Between the articulated bridges or within one of the articulated bridges, an axially movable member is disposed via which the binocular telescope can be focused.